When If is called by using three arguments, the first argument must
evaluate to a value that can be cast as a Boolean. That Boolean value
will determine which of the other two arguments is evaluated and
returned. The following list applies only when the If operator is
called by using three arguments.

...

This statement prints TruePart, because the first argument is true.
Console.WriteLine(If(True, "TruePart", "FalsePart"))
' This statement prints FalsePart, because the first argument is false.
Console.WriteLine(If(False, "TruePart", "FalsePart"))
Dim number = 3
' With number set to 3, this statement prints Positive.
Console.WriteLine(If(number >= 0, "Positive", "Negative"))
number = -1
' With number set to -1, this statement prints Negative.
Console.WriteLine(If(number >= 0, "Positive", "Negative"))